How to render separate monochrome layers?
Actually, monochrome effect can be easily done by ColorRamp node:



To your question:

As you mentioned, it seems that the only problem now is the tilt/side area on the text. I suggest to consider taking the advantage of Material Index here:



To do so:


First, convert the Text objects to mesh (Shortcut is AltC. You may want to remove doubles and correct normal directions after that);
Select all sided faces, then assign a new material to the selection (even can be the exact duplication as the original one, if necessary);
Set a different Pass Index value in setting of this material;
Toggle Material Index passes in Render Layer setting for outputting. You can then use it to separate the tilt/side area and have it controlled separately.




If you don't want to do it for compositing use, using plain materials with Shadelss toggled can also be an easier way:





UPDATE:

Inspired by gandalf3's cool answer, here is the option for outlined result, also with more control by ColorRamp.



You may also consider to generate outlines by FreeStyle, though relatively inefficient and less flexible in this case.